U.S. patent number 7,426,091 [Application Number 11/393,684] was granted by the patent office on 2008-09-16 for magnetic head.
This patent grant is currently assigned to Hitachi Global Storage Technologies Japan, Ltd. Invention is credited to Hiroyuki Hoshiya, Yoshiaki Kawato, Yasuyuki Okada.
United States Patent |
7,426,091 |
Okada , et al. |
September 16, 2008 |
Magnetic head
Abstract
The disclosed invention provides a magnetic head of high
stability in which "erase after write" is prevented. Here is
provided a magnetic head comprising a thin-film magnetic head for
perpendicular magnetic recording, the thin-film magnetic head
including a main pole with its tip facing a magnetic recording
medium and coils for exciting the main pole, wherein the tip of or
at least a part of the main pole consists of a soft magnetic
multilayer containing laminations, each of which comprises a first
ferromagnetic film, a second ferromagnetic film, and an
antiparallel coupling layer formed between the first ferromagnetic
film and the second ferromagnetic film, wherein the antiparallel
coupling layer causes antiferromagnetic interlayer coupling of the
first ferromagnetic film and the second ferromagnetic film.
Inventors: |
Okada; Yasuyuki (Odawara,
JP), Hoshiya; Hiroyuki (Odawara, JP),
Kawato; Yoshiaki (Tokyo, JP) |
Assignee: |
Hitachi Global Storage Technologies
Japan, Ltd (Kanagawa-ken, JP)
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Family
ID: |
32588381 |
Appl.
No.: |
11/393,684 |
Filed: |
March 31, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060164759 A1 |
Jul 27, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10610792 |
Jul 2, 2003 |
7057853 |
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Foreign Application Priority Data
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Dec 20, 2002 [JP] |
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2002-369176 |
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Current U.S.
Class: |
360/125.03;
G9B/5.044 |
Current CPC
Class: |
G11B
5/1278 (20130101) |
Current International
Class: |
G11B
5/147 (20060101) |
Field of
Search: |
;360/125.03,125,125.01,125.12 ;428/212 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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02-061572 |
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Jun 1989 |
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JP |
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07-135111 |
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Nov 1993 |
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JP |
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07-169026 |
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Aug 1994 |
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JP |
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Other References
P Grunberg, J. Barnas, F. Saurenbach, J.A. FuB, A. Wolf and M.
Vohl, "Layered magnetic structures: antiferromagnetic type
interlayer coupling and magnetoresistance due to antiparallel
alignment", Journal of Magnetism and Magnetic Materials, vol. 93,
1991, pp. 58-66. cited by other.
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Primary Examiner: Chen; Tianjie
Attorney, Agent or Firm: Reed Smith LLP Fisher, Esq.;
Stanley P. Marquez, Esq.; Juan Carlos A.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a Continuation application of U.S. application
Ser. No. 10/610,792 filed on Jul. 2, 2003; now U.S. Pat. No.
7,057,853. Priority is claimed based upon U.S. application Ser. No.
10/610,792 filed on Jul. 2, 2003, which claims the priority date of
Japanese Application No. 2002-369176 filed on Dec. 20, 2002, and
which is hereby incorporated by reference.
Claims
What is claimed is:
1. A magnetic head, comprising: a thin-film magnetic head for
perpendicular magnetic recording, said thin-film magnetic head
including a main pole with its tip facing a magnetic recording
medium, wherein the tip of or at least a part of said main pole
includes a soft magnetic multilayer containing laminations, each of
which comprises a first ferromagnetic film, a second ferromagnetic
film, and an antiparallel coupling layer formed between said first
ferromagnetic film and said second ferromagnetic film, wherein said
soft magnetic multilayers include said laminations which are
layered, interleaved with nonmagnetic decoupling films.
2. The magnetic head as recited in claim 1, wherein said main pole
comprises the soft magnetic multilayer in which said laminations
are layered in parallel with a plane facing a magnetic recording
medium.
3. The magnetic head as recited in claim 1, wherein said first
ferromagnetic film and said second ferromagnetic film include at
least one substance among Co, Ni, and Fe.
4. The magnetic head as recited in claim 1, wherein said
antiparallel coupling layer includes at least one substance among
Cr, Ru, Os, Re, Rh, and Cu.
5. The magnetic head as recited in claim 4, wherein said
antiferromagnetic interlayer coupling has a field correspondent to
several dozen to several hundred oersteds.
6. The magnetic head as recited in claim 1, wherein a thickness of
said antiparallel coupling layer falls within a range from 0.5 nm
to 1.2 nm.
7. The magnetic head as recited in claim 1, wherein a thickness of
said antiparallel coupling layer falls within a range from 1.8 nm
to 3 nm.
8. The magnetic head as recited in claim 1, wherein said first
ferromagnetic film and said second ferromagnetic film are
magnetized in antiparallel directions across said antiparallel
coupling layer.
9. The magnetic head according to claim 1, said nonmagnetic
decoupling film includes different materials from what said
antiparallel coupling layer includes.
10. The magnetic head as recited in claim 9, wherein said
nonmagnetic decoupling film includes at least one substance among
Cr, Ru, Os, Rh and Cu.
11. The magnetic head according to claim 1, said nonmagnetic
decoupling film includes material which said antiparallel coupling
layer includes, a thickness of said nonmagnetic decoupling film is
thicker than a thickness of said antiparallel coupling layer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic heads and, more
particularly, to magnetic heads of a perpendicular magnetic
recording type.
2. Description of the Related Art
A magnetic field sensor using antiparallel coupled magnetic films
has been described in Japanese Patent Document 1 as a prior art
reference. It has been discussed in Non-Patent Document 1 that
antiparallel coupling takes place in multilayers or sandwich layers
of Fe/Cr, Fe/Cu, Co/Cr, Co/Ru, and the like. A magnetic multilayer
consisting of multiple layers of soft magnetic films and a magnetic
head in which such a magnetic multilayer is employed to constitute
a magnetic pole or a yoke have been described in Japanese Patent
Document 2 as a prior art reference. A spin-valve sensor using
antiferromagnetically coupled films has been described in Japanese
Patent Document 3 as a prior art reference.
[Japanese Patent Document 1]
Japanese Unexamined Patent Application Publication No. Hei
2-61572
[Japanese Patent Document 2]
Japanese Unexamined Patent Application Publication No. Hei
7-135111
[Japanese Patent Document 3]
Japanese Unexamined Patent Application Publication No. Hei
7-169026
[Non-Patent Document 1]
Journal of Magnetism and Magnetic Materials, 93 (1991), pp.
58-66
BRIEF SUMMARY OF THE INVENTION
Prior art magnetic head technology has limitations in producing
magnetic recording devices with a sufficiently high recording
density, particularly, in producing magnetic heads with good
performance enough to perform submicron trackwidth magnetic
recording and read such tracks accurately, and it has been
difficult to achieve functionality as a storage device. The reason
lies in the properties of soft magnetic films and the demagnetizing
field thereof. In order to allow magnetic action to take place at a
high frequency and with sufficient sensitivity and stability,
so-called soft magnetic thin films having a high permeability are
necessary.
Nowadays, however, with great enhancement in magnetic recording
density, recording bits are becoming smaller and smaller in the
order of submicrons and the stable performance of soft magnetic
thin films is becoming difficult to sustain. The reason is that, at
the ends of the soft magnetic films by which smaller magnetic
circuits have been formed, a magnetic domain structure is produced
by the demagnetizing fields of the soft magnetic films and such a
magnetic domain affects magnetic recording performance. Especially,
perpendicular recording type thin-film magnetic heads have suffered
from the following problem. The magnetic pole comes to have the
magnetic domain structure after recording action is performed and
the resultant remnant magnetization in the magnetic pole erases or
disturbs information recorded as magnetized bits on a recording
medium.
As a method for reducing the influence of the demagnetizing fields,
a technique has heretofore been known that stacks soft magnetic
films and non-magnetic films to form a multilayer and generates
magnetostatic coupling in the ends of the multilayer for single
domain formation. However, as the single domain formation by the
magnetostatic coupling results from the magnetostatic coupling in
the ends of the multilayer, accordingly, the coupling force is weak
and a sufficient effect is not obtained.
In a multilayer in which non-magnetic metal layers and
ferromagnetic metal layers are stacked alternately, such a
phenomenon has lately been found that the ferromagnetic metal
layers are antiferromagnetically coupled across a non-magnetic
metal layer. Here, the "antiferromagnetic coupling" means that, in
adjacent ferromagnetic layers, coupling energy is generated such
that their magnetization acts in antiparallel directions with each
other across the in-between non-magnetic metal layer. Through
application of this phenomenon, magnetic sensors and the like have
been proposed, as typically described in Japanese Patent Document 4
as a prior art reference specified below:
Japanese Patent Document 4, Japanese Unexamined Patent Application
Publication No. Hei 2-61572
Although the physical reason for the phenomenon of mutually
antiparallel magnetization coupling occurring in multilayer films
has not been well explained, it is experimentally known that the
above phenomenon occurs with combination of specific materials and
thickness. For example, Non-Patent Document 1 states that
antiparallel coupling takes place in multilayers or sandwich layers
of Fe/Cr, Fe/Cu, Co/Cr, Co/Ru, and the like.
More specifically, depending on the thickness of the in-between
non-magnetic film, for example, a Cr film, the force of the above
antiparallel coupling of the ferromagnetic films across the
non-magnetic film increases and decreases as close as fluctuation
or is generated or lost. It is known that stable antiparallel
coupling of the ferromagnetic films takes place when the thickness
of the in-between non-magnetic film such as the Cr film is around 1
nm and in a range of 2-3 nm. As a proposal of application of this
phenomenon to magnetoresistive sensors, Japanese Patent Document 3
described a spin valve sensor using antiferromagnetically coupled
films.
In the present invention, in order to provide a magnetic head
capable of a high recording density, a soft magnetic film structure
which is employed in the above magnetic head, especially, a main
pole in a perpendicular recording head structure is constituted by
a multilayer consisting of soft magnetic and ferromagnetic films
which are antiferromagnetically coupled.
Essentially, the present invention provides a magnetic head
comprising a thin-film magnetic head for perpendicular magnetic
recording, the thin-film magnetic head including a main pole with
its tip facing a magnetic recording medium and coils for exciting
the main pole, wherein the tip of or at least a part of the main
pole consists of a soft magnetic multilayer containing laminations,
each of which comprises a first ferromagnetic film, a second
ferromagnetic film, and an antiparallel coupling layer formed
between the first ferromagnetic film and the second ferromagnetic
film, wherein the antiparallel coupling layer causes
antiferromagnetic interlayer coupling of the first ferromagnetic
film and the second ferromagnetic film.
In order to obtain the soft magnetic multilayer in which the
ferromagnetic films are antiferromagnetically coupled, the above
multilayer comprises minimum sets of ferromagnetic, antiparallel
coupling, and ferromagnetic films, and the ferromagnetic films and
the antiparallel coupling film are made of predetermined materials,
respectively, and formed in a planar stratified structure with
predetermined thicknesses per film.
Also, a return pole and magnetic shields may be constituted by the
foregoing soft magnetic multilayer in which ferromagnetic films are
antiferromagnetically coupled, respectively.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an example of structure of the soft magnetic multilayer
employed in the magnetic head of the present invention.
FIGS. 2A and 2B show comparison in magnetic properties between the
soft magnetic multilayer employed in the present invention and a
commonly employed soft magnetic layer.
FIG. 3 shows magnetization curves of a FeCo/Cr/FeCo multilayer as
the Cr film thickness varies.
FIGS. 4A and 4B show change in remnant magnetization proportion and
saturation magnetic field Hs* with change in the Cr film thickness
and the FeCoNi film thickness.
FIG. 5 shows magnetization curves of FeCo/Cr/FeCo and FeCo/Ru/FeCo
multilayers.
FIG. 6 shows change in antiparallel exchange coupling energy with
change in the Ru film thickness.
FIG. 7 shows change in antiparallel exchange coupling field for an
NiFe/Cr/NiFe multilayer with change in the Cr film thickness.
FIG. 8 shows relationship between saturation magnetic field energy
and magnetization quantity in ferromagnetic films for a variety of
material combinations of ferromagnetic films and an antiparallel
coupling film.
FIGS. 9A through 9D show magnetization curves for a multilayer of
FeCo (25 nm)/CrFeCo (1 nm)/FeCo (25 nm) as the dose of FeCo doped
into the Cr antiparallel coupling film changes.
FIG. 10 shows change in saturation magnetic field energy and
remanant magnetization proportion for the multilayer of FeCo (25
nm)/CrFeCo (1 nm)/FeCo (25 nm) with change in the dose of FeCo
doped into the Cr film.
FIGS. 11A and 11B show magnetization curves for a multilayer
example in which a NiCr film is employed as the underlayer and for
a multilayer example without the underlayer.
FIG. 12 shows an example of structure of a magnetic head for
perpendicular recording in which the soft magnetic multilayer in
which ferromagnetic films are antiferromagnetically coupled in
accordance with the present invention is employed to constitute the
main pole.
FIG. 13 shows another example of structure of a magnetic head for
perpendicular recording in which the soft magnetic multilayer in
which ferromagnetic films are antiferromagnetically coupled in
accordance with the present invention is employed to constitute the
main pole.
FIG. 14 shows an example of structure of a magnetic recording and
readback device using the magnetic head of the present
invention.
FIGS. 15A and 15B show graphs plotting measurements of an "erase
after write" fault incidence, measured for samples of the magnetic
head for perpendicular recording in which the soft magnetic
multilayer in which ferromagnetic films are antiferromagnetically
coupled in accordance with the present invention is employed in the
main pole.
FIGS. 16A through 16E show schematic diagrams of magnetization
states of the main pole of a perpendicular magnetic recording head
for explaining the effect and principles of the present
invention.
FIG. 17 shows an example of structure of a perpendicular magnetic
recording head in which the soft magnetic multilayer in which
ferromagnetic films are antiferromagnetically coupled in accordance
with the present invention is employed to constitute the return
pole.
FIG. 18 shows an example of structure of a perpendicular magnetic
recording head in which the soft magnetic multilayer in which
ferromagnetic films are antiferromagnetically coupled in accordance
with the present invention is employed to constitute the magnetic
shields.
FIG. 19 shows an example of structure of a longitudinal magnetic
recording head in which the soft magnetic multilayer in which
ferromagnetic films are antiferromagnetically coupled in accordance
with the present invention is employed to constitute the tip of an
upper magnetic core.
FIG. 20 shows another example of structure of the soft magnetic
multilayer employed in the magnetic head of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As a magnetic head to which the present invention applies, for
example, there is provided a magnetic head comprising a thin-film
magnetic head for perpendicular magnetic recording, the thin-film
magnetic head including a main pole with its tip facing a magnetic
recording medium and coils for exciting the main pole, wherein the
tip of or at least a part of the main pole consists of a soft
magnetic multilayer containing laminations, each of which comprises
a first ferromagnetic film, a second ferromagnetic film, and an
antiparallel coupling layer formed between the first ferromagnetic
film and the second ferromagnetic film, wherein the antiparallel
coupling layer causes antiferromagnetic interlayer coupling of the
first ferromagnetic film and the second ferromagnetic film.
The materials of the ferromagnetic films and in-between
antiparallel coupling film are determined, according to
predetermined combinations. If the ferromagnetic films are of a
body centered cubic structure, it is desirable that the
antiparallel coupling film comprises Cr or Ru as its principal
constituent. Instead of Ru, Os, Ir, Re, or Rh may be used to obtain
the same effect. It may be preferable, if appropriate, to dope
another element such as, for example, Fe into a Cr or Ru film to
reduce the antiferromagnetic coupling energy, provided the dose of
the dopant should be 20 atomic percent and below.
If the ferromagnetic films are of a face centered cubic structure,
it is desirable that the antiparallel coupling film comprises Ru as
its principal constituent. Instead of Ru, Os, Ir, Re, Rh, or Cu may
be used to obtain the same effect. It may be preferable, if
appropriate, to dope another element such as, for example, Fe into
an Ru film to reduce the antiferromagnetic coupling energy,
provided the dose of the dopant should be 20 atomic percent and
below.
In either cases, when the thickness of the antiparallel coupling
film falls within a range of 0.5-1.2 nm or a range of 1.8-3 nm,
stable antiferromagnetic coupling energy is obtained.
The above soft magnetic multilayer in which ferromagnetic films are
antiferromagnetically coupled must be formed in a planar stratified
structure with minimized concavity and convexity so that what is
called an orange-peel effect which impedes the antiferromagnetic
coupling does not take place. To accomplish this, it is necessary
to optimize the conditions for fabricating the soft magnetic
multilayer and the ferromagnetic film thickness must be limited to,
specifically, one micron and less. Besides, it is preferable to
form a NiCr underlayer or the like, about 5 nm thick, under the
multilayer in order to prevent crystal grains from becoming too
coarse in the soft magnetic multilayer.
In an example in which a ferromagnetic multilayer of the present
invention is employed in a magnetic head for perpendicular
recording, reversal of magnetization of a magnetic pole must take
place readily in response to an external magnetic field. In view
hereof, the ferromagnetic multilayer must be configured to have a
proper value of antiferromagnetic interlayer coupling.
Specifically, proper combinations of the materials and thickness of
the ferromagnetic films and the antiparallel coupling film should
be used. Moreover, the ferromagnetic multilayer thickness should be
10 nm and above, and the dose of a dopant to the antiparallel
coupling film should be 20 atomic percent and below. Having been
designed in this way, the soft magnetic multilayer will be capable
of having antiferromagnetic coupling having a field correspondent
to several dozen to several hundred oersteds and a magnetic head
with a high permeability and stable performance can be
realized.
With reference to the accompanying drawings, an example of the
magnetic head to which the present invention applies will be
described in detail hereinafter.
Thin films constituting the soft magnetic multilayer of the present
invention were formed by an rf (radio-frequency) magnetron
sputtering apparatus as will be described below.
In an atmosphere of 1 to 6 mTorr argon, on a ceramics substrate,
the multilayer films were formed by sequentially depositing the
layers of the following materials. As sputtering targets, nickel
plus 20 at % Cr alloy, copper, iron plus 30 at % cobalt, chromium,
and ruthenium targets were used. A 1 cm square chip of Ni or the
like was disposed on the iron plus cobalt target, if appropriate,
and a FeCoNi film was deposited. The multilayer was formed such
that plasma was generated inside the apparatus by applying rf power
to the cathodes on which the targets were disposed respectively and
the layers were formed sequentially by opening the shutters of the
cathodes in sequence. Co-sputter applied to some of film
deposition; that is, the chromium target and the FeCo target were
discharged at the same time to form a chromium and FeCo alloy
layer.
During film deposition, by using a permanent magnet, a magnetic
field of about 6.4 kA/m (80 oersteds) was applied in parallel to
the substrate, thus inducing uniaxial magnetic anisotropy. The
elements on the substrate were formed by being patterned through a
photoresist process. Then, the substrate was integrated with a
slider and mounted on the host magnetic recording device. Specific
embodiments of the present invention will be explained hereinafter
by following the drawings.
FIG. 1 is an example of structure of the soft magnetic multilayer
employed in the magnetic head of the present invention. A soft
magnetic multilayer 10 in which ferromagnetic films are
antiferromagnetically coupled is formed such that an underlayer 14
is formed on a substrate 50 and sets of a ferromagnetic film (first
ferromagnetic film) 15, an antiparallel coupling film 153, and a
ferromagnetic film (second ferromagnetic film) 15 are layered in
order repeatedly. The material, thickness, and deposition condition
of the antiparallel coupling film are adjusted so that
antiferromagnetic coupling energy is exerted to make adjacent
ferromagnetic films 15 magnetized in directions antiparallel with
each other across the antiparallel coupling film 153. The details
hereof will be described later.
Though the use of the above multilayer in which ferromagnetic films
are antiferromagnetically coupled, stable antiparallel magnetic
domain states can be achieved. For example, by observing magnetic
domain states from the air-bearing surface of the magnetic head
through Spin-SEM or Magnetic Energy Microscopy (MFM), antiparallel
closed domains can be found. Even in the case of simply
multilayered films, closed domain states can also be found
partially. However, stable closed domain states can be realized by
the present invention.
FIG. 2 shows comparison in magnetic properties between the soft
magnetic multilayer employed in the present invention and a
commonly employed soft magnetic layer. FIG. 2A shows a
magnetization curve along an easy axis of magnetization for the
soft magnetic multilayer employed in the present invention, wherein
FeCo films are used as ferromagnetic films and two layers of FeCo
films are antiferromagnetically coupled across a 1 nm thick Cr
antiparallel coupling film. It is seen that the magnetization curve
is plotted symmetrically in the positive and negative domains of
the magnetic field as if the curve was divided into two loops,
which represents mutually antiparallel vectors of magnetization in
the two layers of FeCo films under the effect of the
antiferromagnetic coupling energy.
Magnetic energy increase up to saturation in the magnetic field
found in this magnetization curve is a value determined by the
thickness and structure of the ferromagnetic films and antiparallel
coupling film, not a physical quantity proper to the ferromagnetic
films like what is called an anisotropy field due to uniaxial
magnetic anisotropy. Although integration of the magnetization
curve should be performed for precise evaluation of
antiferromagnetic coupling, here, a line approximating the
magnetization curve as shown in FIG. 2A is simply drawn to follow
the increase of magnetization up to saturation and thereby a value
of saturation magnetic field Hs* is obtained.
The reason is that the value of saturation magnetic field Hs*
virtually describes the magnetization curve of the soft magnetic
multilayer employed in the present invention and, if, for example,
saturation flux density Bs (in units of Teslas) is used, an
effective permeability of the soft magnetic multilayer having
saturation magnetic field Hs* (in oersteds) is approximately
evaluated by "permeability.about.Bs.times.10000/Hs*."
Meanwhile, a magnetization curve of the FeCo single-layer film
example in which the antiparallel coupling film is not used is
shown FIG. 2B for comparison. Unlike the curve shown in FIG. 2A, no
significant saturation magnetic field is found in the magnetization
curve shown in FIG. 2B. This is because the anisotropy field due to
uniaxial magnetic anisotropy is found in the single-layer film, but
its magnetization is generally as strong as 20 oersteds and
below.
Whether antiferromagnetic coupling takes place, using the
antiparallel coupling film can be known from the form of the
magnetization curve as shown in FIG. 2, and also distinguishable
from the multilayer structure if the magnetization curve cannot be
obtained by measurements. The multilayer structure which provides
proper antiparallel coupling will be explained below.
FIG. 3 shows magnetization curves of a FeCo/Cr/FeCo multilayer as
the Cr film thickness varies. It is seen that great change occurs
in the magnetization curves when the Cr film thickness varies in a
range of 0.9 to 1.1 nm. It is also seen that the magnetization
curve when the Cr film is 0.9 nm thick has a large proportion of a
remnant magnetization component and antiparallel coupling is not
uniform. When the Cr film thickness has increased from 0.95 to 1,
the remnant magnetization component becomes virtually zero and Hs*
increases. As the Cr film becomes even thicker, Hs* decreases
inversely.
FIG. 4 shows change in remnant magnetization proportion and
saturation magnetic field Hs* with change in the Cr film thickness
and the FeCoNi film thickness. FIG. 4A shows the above change with
change in the Cr film thickness. It is seen that, as the
antiparallel coupling layer, the Cr film thicknesses from 0.95 to
1.1 nm are good and 1.0 nm is the best among others.
Similarly, FIG. 4B shows the corresponding change for a
FeCoNi/Cr/FeCoNi multilayer with change in the FeCoNi film
thickness. When the FeCoNi film is as thin as 10 nm, Hs* is as
great as 300 oersteds. However, Hs* decrease as the FeCoNi film
becomes thicker. Up to the FeCoNi film thickness of 30 nm, the
remanant magnetization is little and there is a good antiparallel
coupling state. However, for 40 nm and thicker FeCoNi films, Hs* is
virtually zero and the remanant magnetization proportion is almost
1; that is, there is a state of none of antiparallel coupling.
Essentially, the energy of antiparallel coupling is determined by
combinations of ferromagnetic films and an antiparallel coupling
film and multilayer structure. The result of FIG. 4B is considered
attributable to two factors. One factor is the fact that, as the
ferromagnetic film thickness becomes thicker, the magnetic field
which induces antiparallel coupling decreases inversely if the
antiparallel coupling energy is constant. This is because the
antiparallel coupling energy is the product of the quantity of
magnetization in the ferromagnetic film=saturation flux
density.times.thickness and the saturation magnetic field.
The other factor is that, with increase of the multilayer
thickness, concavity and convexity in the multilayer increase,
which produces an effect that magnetostatic coupling, what is
called the orange-peel effect, takes place between adjacent
ferromagnetic films and cancels the antiparallel coupling. Although
such an effect of concavity and convexity can be mitigated to some
degree by optimizing the conditions for fabricating the multilayer,
our experiments indicated that antiparallel coupling is lost for
40-60 nm and thicker ferromagnetic films and a total multilayer
thickness of 1.0 to 0.2 .mu.m and thicker.
FIG. 5 shows magnetization curves of FeCo/Cr/FeCo and FeCo/Ru/FeCo
multilayers, where the FeCo films are 10 nm thick, Cr film is 1.0
nm, and Ru film is 0.8 nm thick. In the case of employing the Cr
film, Hs* is about 300 oersteds; whereas, in the case of employing
the Ru film, Hs* is about 600 oersteds. It was found that the
antiparallel coupling energy in the case of employing the Ru film
is almost double that energy in the case of employing the Cr
film.
FIG. 6 shows change in antiparallel exchange coupling energy with
change in the Ru film thickness. The following characteristic was
obtained. In the Ru film thickness range of 0.6 to 1.0 nm,
antiparallel coupling takes place and its effect is good in the Ru
film thickness range of 0.7 to 0.9 nm and the best with the Ru film
thickness of 0.8 nm. Also, weak coupling energy was found around
the Ru film thickness of 2 nm. As indicated from this result, the
antiparallel coupling film thickness is, of course, a factor of
changing the saturation magnetic field. Because antiparallel
exchange coupling is quite sensitive to the thickness of the
antiparallel coupling film as described for FIGS. 3, 4, 6, and 7,
it is desirable to form the antiparallel coupling film with a
thickness for which a peak of great stable coupling energy is
obtained. Therefore, the antiparallel coupling film thickness
should be determined properly, according to what material the film
is made of.
FIG. 7 shows change in antiparallel exchange coupling field for an
NiFe/Cr/NiFe multilayer with change in the Cr film thickness.
Although the maximum antiparallel exchange coupling energy is
obtained with the Cr film thickness of 1 nm as is the case for the
FeCoNi/Cr/FeCoNi multilayer, the NiFe/Cr/NiFe multilayer differs
from the FeCoNi/Cr/FeCoNi multilayer in that its saturation
magnetic field is as small as 20 oersteds. As explained above, a
variety of material combinations and thicknesses of ferromagnetic
films and an antiparallel coupling film leads to variation in both
the antiparallel coupling and the saturation magnetic field. Thus,
best material combination and thicknesses of these films for best
magnetic properties should be needed to obtain a soft magnetic
multilayer capable of desirable antiparallel coupling
performance.
FIG. 8 shows relationship between saturation magnetic field and
magnetization of ferromagnetic films for a variety of material
combinations of ferromagnetic films and an antiparallel coupling
film. The magnetization of ferromagnetic films is represented by
the product of ferromagnetic film thickness and saturation flux
density.
The saturation magnetic field decreases as the magnetic film
thickness increases, which differs, according to ferromagnetic film
and antiparallel coupling film material combinations. Thus, proper
selection from a variety of material combinations and thicknesses
of ferromagnetic films and an antiparallel coupling film is needed
to obtain a soft magnetic multilayer with properly set saturation
magnetic field.
Preferable material combinations of ferromagnetic films and an
antiparallel coupling film with experimental values of antiparallel
coupling film thickness and saturation magnetic field energy change
conjectured to occur with each material combination are shown in
FIG. 8. Meanwhile, an optimum value of saturation magnetic field
can be determined from a viewpoint of soft magnetism. Simply
speaking, permeability of a soft magnetic multilayer is determined
by 10000.times.saturation flux density (in Teslas)/saturation
magnetic field (in oersteds). Saturation flux density for
ferromagnetic films is a maximum of 2.4 T in the case of FeCo films
and 1 T in the case of NiFe films and, therefore, is not a factor
that greatly differs with film compositions as compared with other
factors.
If a lower limit of required permeability is assumed to be 50, this
value would be the lower limit for all kinds of soft magnetic
thin-film multilayers. Similarly, a lower limit of saturation
magnetic field is considered to be 20 oersteds. This is because the
anisotropy magnetic field energy for a CoNiFe alloy thin-film
multilayer is about 20 oersteds and, if the saturation magnetic
field energy is lower than this value, the anisotropy magnetic
field will be dominant and likely to suppress antiparallel
coupling.
If saturation flux density is assumed to be 2 T, upper and lower
limits of saturation magnetic field can be defined from the above
relation and saturation magnetic field should be set at 400
oersteds and below. The reason is that, with 400 oersteds and
higher saturation magnetic field, permeability will be virtually 50
and below even if saturation flux density is 2 T and, consequently,
the soft magnetic multilayer functionality will be disabled. As
seen from FIG. 4B, with 50 nm and thicker ferromagnetic films, the
remanant magnetization proportion rises and, in such cases, also,
the soft magnetic multilayer functionality will be disabled.
Conversely, with 5 nm and thinner soft magnetic multilayer
structures, the volume of the soft magnetic multilayer is
insufficient and the flux transmission function of the layer will
be disabled. This disability can be rectified to some degree by
further layering multiple ferromagnetic films of 5 nm thick and
less, but, in this case, the number of antiparallel coupling films
increases accordingly and this results in decrease in the total
flux density and cost increase for multiple times of layer
deposition.
In order to satisfy the above-discussed requirements, bounds
corresponding to a bold rectangular marked off in the graph FIG. 8
should be put to the formation of the soft magnetic multilayer
employed in the present invention; that is, within a range of
20-400 oersteds of saturation magnetic field and within a range of
5-50 nm of ferromagnetic film thickness.
According to what material the antiparallel coupling film is made
of, the above bounds to be satisfied are more restricted. For the
combination of FeCoNi ferromagnetic films and a Cr (1 nm)
antiparallel coupling film, the ferromagnetic film thickness is
further restricted to a range of about 20-50 nm to be
satisfied.
Meanwhile, for the combination of CoFe ferromagnetic films and an
Ru (0.8 nm) antiparallel coupling film, all portions of its curve
do not satisfy the bounds even if the ferromagnetic film thickness
is altered. Film material combinations to satisfy the above bounds
are tabulated in Table 1. The table includes saturation flux
density Bs for ferromagnetic films and crystal structure. This is
because, even with minor charge in ferromagnetic film composition
and with different dopant elements, the kinds of multilayers
exhibit almost the same properties, provided Bs and crystal
structure do not change much.
TABLE-US-00001 TABLE 1 Antiparallel Bs of Ferromagnetic film
coupling ferromagnetic Crystal (thickness) film (thickness) film
structure FeCoNi (20-50 nm) Cr (1 nm) 2.0 T bcc FeCo (5-20 nm) Ru
(1.8-2.0 nm) 2.4 T bcc FeCo (30-50 nm) Ru (0.8 nm) 2.4 T bcc NiFe
(40-50 nm) Ru (0.8 nm) 1.0 T fcc CoFe (non-proper value) Ru (0.8
nm) 1.8 T fcc
In the meantime, antiferromagnetic coupling energy can be
controlled somewhat by doping another element into the antiparallel
coupling film. FIG. 9 shows magnetization curves for a multilayer
of FeCo (25 nm)/CrFeCo (1 nm)/FeCo (25 nm) as the dose of FeCo
doped into the Cr antiparallel coupling film changes. The following
can be seen. With the dose of zero, saturation magnetic field
energy of about 200 oersteds is obtained. As the dose of FeCo doped
into the Cr film increases, the magnetization curve changes in
which saturation magnetic field energy gradually decreases. When
the dose of FeCo has reached 20 at %, there is almost no indication
of antiferromagnetic coupling in the magnetization curve and
remanant magnetization increases.
FIG. 10 shows change in saturation magnetic field energy and
remanant magnetization proportion for the multilayer of FeCo (25
nm)/CrFeCo (1 nm)/FeCo (25 nm) with change in the dose of FeCo
doped into the Cr film. The following can be seen. As the dose
increases, the saturation magnetic field energy decreases and can
be controlled to a half as much as the value of that energy with
the dose of zero. However, in the domain of quite low saturation
magnetic field with higher dose, a steep decrease of that energy
with the rise of the dose and a steep increase in remanant
magnetization proportion are found and, probably, proper properties
are not obtained. Accordingly, the result of FIG. 10 indicated that
proper doses of a dopant be 20 at % and below and saturation
magnetic field can be decreased down to a half as much as the value
of that energy for the multilayer without being doped.
Further, the underlayer under the soft magnetic multilayer employed
in the present invention will be described. In FIG. 1, the
underlayer 14 is positioned under the soft magnetic multilayer of
the present invention. FIG. 11 shows magnetization curves for a
multilayer example in which a NiCr film is employed as the
underlayer and for a multilayer example without the underlayer. The
magnetization curve for the multilayer example in which the
underlayer is employed, as explained for FIG. 2, clearly reflects
antiferromagnetic coupling, whereas the magnetization curve for the
multilayer example without the underlayer indicates increase in
coercivity and antiferromagnetic coupling which is, however, not
clear comparatively. This is because coercivity as much as
saturation magnetic field induces a remanant magnetization
component and, consequently, sufficient soft magnetic properties
are not obtained in spite of a certain quantity of
antiferromagnetic coupling energy. Therefore, it is advisable to
employ a suitable underlayer such as NiCr and the like. Besides the
NiCr film, Ti, Cr, Ru, and the like can produce the same effect to
some degree.
Magnetic head embodiments using the above-described soft magnetic
multilayer in which ferromagnetic films are antiparallel coupled
will be explained hereinafter. FIG. 12 shows an example of
structure of a magnetic head for perpendicular recording in which
the soft magnetic multilayer in which ferromagnetic films are
antiferromagnetically coupled in accordance with the present
invention is employed to constitute the main pole. On the substrate
50 which is integrated with the slider, a lower magnetic shield 35,
an electrode 40, and a magnetoresistive multilayer 101 are formed
and, moreover, another electrode 40 and an upper magnetic shield 36
are formed, and a read gap 43 which senses a readback signal is
formed. While a TMR or CPP-GMR type readback sensor which causes
current to flow in a layer thickness direction is shown here as a
readback unit, it is possible to use another type of readback
sensor such as GMR readback sensors which cause current to flow in
an in-plane direction as the readback unit without altering the
essential characteristics of the present invention.
The recording head further includes a return pole 84, coils 42, and
a main pole 83 which form a magnetic circuit. In FIG. 12, the main
pole 83 consists of a soft magnetic multilayer 10 in which
ferromagnetic films are antiparallel coupled. On the underlayer 14,
sets of the ferromagnetic film 15, antiparallel coupling film 153,
and ferromagnetic film 15 are layered in order. It is preferable to
stack 4-12 layers of ferromagnetic films 15 in the main pole. With
a small number of layers, there is the fear of reducing the effect
that magnetization and reverse magnetization cancel each other at
the ends of the magnetic pole. With too many layers, the recording
capability decreases. Thus, 6 to 8 layers are most desirable. It is
desirable to stack an even number of ferromagnetic film layers so
that magnetization and reverse magnetization will cancel each other
between adjacent two among the ferromagnetic films disposed to be
magnetized in antiparallel directions. On the magnetic head, an
air-bearing surface 63 is formed which approaches a magnetic
recording medium and performs magnetic recording and readback.
FIG. 13 shows another example of structure of a magnetic head for
perpendicular recording in which the soft magnetic multilayer in
which ferromagnetic films are antiferromagnetically coupled in
accordance with the present invention is employed to constitute the
main pole. On the substrate 50 which is integrated with the slider,
the lower magnetic shield 35, one electrode 40, and the
magnetoresistive multilayer 101 are formed and, moreover, another
electrode 40 and the upper magnetic shield 36 are formed, and the
read gap 43 which senses a readback signal is formed. While the TMR
or CPP-GMR type readback sensor which causes current to flow in the
layer thickness direction is shown here as the readback unit, it is
possible to use another type of readback sensor such as GMR
readback sensors which cause current to flow in the in-plane
direction as the readback unit without altering the essential
characteristics of the present invention.
The recording head further includes the return pole 84, coils 42, a
first main pole 831, and a second main pole 832 which form a
magnetic circuit. In FIG. 13, the first main pole 831 consists of
the soft magnetic multilayer 10 in which ferromagnetic films are
antiparallel coupled. On the underlayer 14, sets of the
ferromagnetic film 15, antiparallel coupling film 153, and
ferromagnetic film 15 are layered in order. It is preferable to
stack 4-12 layers of ferromagnetic films 15 in the main pole. With
a small number of layers, there is the fear of reducing the effect
that magnetization and reverse magnetization cancel each other at
the ends of the magnetic pole. With too many layers, the recording
capability decreases. Thus, 6 to 8 layers are most desirable. It is
desirable to stack an even number of ferromagnetic film layers so
that magnetization and reverse magnetization will cancel each other
between adjacent two among the ferromagnetic films disposed to be
magnetized in antiparallel directions. On the magnetic head, the
air-bearing surface 63 is formed which approaches a magnetic
recording medium and performs magnetic recording and readback.
FIG. 14 shows an example of structure of a magnetic recording and
readback device using the magnetic head of the present invention. A
disk 95 which supports a recording medium 91 on which information
is magnetically recorded is rotated by a spindle motor 93. A head
slider 90 is moved and positioned on a track of the disk 95 by an
actuator 92. In the magnetic disk drive, a read head and a
recording head integrated into the head slider 90 approach specific
recording locations on the disk 95 by this mechanism and
sequentially write signals onto and read signals from the medium
through magnetic interaction.
It is preferable that the actuator 92 is a rotary actuator. Write
signals received through a signal processing unit 94 are recorded
on the medium by the recording head and an output of the read head
is passed through the signal processing unit 94 and retrieved as a
signal. When the read head is moved to a target recording track, a
high sensitivity output from the read head is used to detect a
specific position on the track and control the actuator so that the
actuator can position the head slider. While the head slider 90 and
the disk 95 are single each in FIG. 14, the device may include a
plurality of head sliders and disks. The disk 95 may have a double
sided recording medium 91 on which information may be recorded. If
information is recorded on either sides of the disk, two head
sliders 90 are disposed on the either sides of the disk.
FIG. 15 shows graphs plotting measurements of an "erase after writ"
fault incidence, measured for samples of the magnetic head for
perpendicular recording in which the soft magnetic multilayer in
which ferromagnetic films are antiferromagnetically coupled in
accordance with the present invention is employed in the main pole.
FIG. 15A is a graph of the above measurements made for magnetic
heads with the thickness of the Cr film which should be the
antiparallel coupling layer varying from 0.5 nm to 5 nm, in which
antiferromagnetic coupling energy is changed and lost, and a
magnetic head using the main pole in which the Cr film thickness is
0 nm, that is, a a single layer structure, which were produced as
samples.
For the magnetic head with the single monolayer main pole, the
fault incidence is almost 100% and magnetic recording would be
impossible to achieve with this head. For the heads with 0.5-1.3 nm
thick Cr films, the fault incidence decreased to 50% and below.
Especially, for the head with 1 nm thick Cr films, the fault
incidence decreased to 25% and below. This indicates that the use
of the soft magnetic multilayer in which ferromagnetic films are
antiferromagnetically coupled in the main pole is significantly
effective for suppressing the "erase after write" faults. There is
also shown a tendency that the fault incidence increases as the Cr
thickness increases to 1.3 nm and above. For the magnetic heads
using the multilayer main pole in which Cr films are so thick, 2 nm
and thicker, as to impede antiferromagnetic coupling, the fault
incidence is about 80%, thus indicating that normal recording is
not performed, though these heads have little effect on improving
the fault incidence.
FIG. 15B is a graph of the above fault incidence measurements for
heads produced as samples in which a total magnetic film (FeCoNi)
thickness in the multilayer is fixed to 200 nm and thickness per
FeCoNi layer and the number of layers vary. That is, if thickness
per FeCoNi layer is 25 nm, eight layers are stacked; if 33 nm, six
layers are stacked in the produced head. Besides, the FeCoNi layers
are interleaved with 1 nm thick Cr films to provide maximum
antiferromagnetic coupling. With 40 nm and thinner FeCoNi films,
all heads show the fault incidence of 25% and below. However, it is
apparent that, with 50 nm and thicker FeCoNi films, the fault
incidence approximates to 100%. Accordingly, thickness per magnetic
layer must be restricted to 50 nm and below.
Meanwhile, as shown in FIG. 4B, there is a tendency that saturation
magnetic field energy increases with decrease in the magnetic layer
thickness. Through consideration of this result, there is the fear
of overwrite deteriorating when the above magnetic films are used
in the head. In FIG. 15B, it is seen that sufficient overwrite
performance is obtained even with 10 nm thick FeCoNi films. Drawing
a conclusion from the above results, 10-50 nm magnetic films are
preferable in the multilayer magnetic pole in which these films are
antiferromagnetically coupled.
FIG. 16 shows schematic diagrams for explaining the effect of the
present invention. In an example in which the main pole of a
perpendicular magnetic recording head consists of a single layered
ferromagnetic film, after a recording action, the main pole is
magnetized in a magnetic domain state where there is a
magnetization vector towards the magnetic recording medium, as
shown in FIG. 16A. The magnetization state where magnetization
towards the recording medium exists is considered as a cause of
"erase after write" faults.
For a multilayer main pole consisting of ferromagnetic films, as
shown in FIG. 16B, the films are arranged such that they can be
magnetized in antiparallel directions with each other, thus making
it possible to reduce magnetic flux intrusion to the recording
medium. However, in the simply multilayered structure, only
demagnetizing fields generated at the ends of the main pole are to
produce the state where the films are magnetized in antiparallel.
In perpendicular magnetic recording, because a soft magnetic film
is employed as the underlayer of the recording medium, it is
possible that the magnetic flux is transmitted from the edge of the
main pole to the underlayer (FIG. 16C) and it is difficult to
produce the desirable closed magnetization state only by the
demagnetizing fields generated at the ends of the main pole.
For the magnetic head employing the soft magnetic multilayer in
which ferromagnetic films are antiferromagnetically coupled in
accordance with the present invention, magnetic properties for
producing antiparallel magnetization, that is, antiferromagnetic
coupling takes place in the soft magnetic multilayer, as shown in
FIG. 16D. Thus, the desired stable magnetization state can be
produced in the magnetic pole of the perpendicular magnetic
recording head. In this case, between ferromagnetic films in the
multilayer, antiferromagnetic coupling exists in addition to
magnetostatic coupling at the ends of the main pole, an the
multilayer structure as shown in FIG. 16D has the advantage of
preventing the magnetic domain states that cause "erase after
write" faults.
The soft magnetic multilayer in which ferromagnetic films are
antiferromagnetically coupled, used in the present invention has
the advantage of producing the stable magnetization state where the
films are magnetized in antiparallel with each other. Thus, the
above multilayer has the advantage of preventing undesirable
magnetic domain states generated by demagnetizing fields which are
often found in soft magnetic films having patterned ends. With
these advantages, the above multilayer can have other applications
than the main pole of the perpendicular magnetic recording
head.
FIG. 17 shows an example of structure of a perpendicular magnetic
recording head in which the soft magnetic multilayer in which
ferromagnetic films are antiferromagnetically coupled in accordance
with the present invention is employed to constitute the return
pole. On the substrate 50 which is integrated with the slider, the
lower magnetic shield 35, one electrode 40, and the
magnetoresistive multilayer 101 are formed and, moreover, another
electrode 40 and the upper magnetic shield 36 are formed, and the
read gap 43 which senses a readback signal is formed. While the TMR
or CPP-GMR type readback sensor which causes current to flow in the
layer thickness direction is shown here as the readback unit, it is
possible to use another type of readback sensor such as GMR
readback sensors which cause current to flow in the in-plane
direction as the readback unit without altering the essential
characteristics of the present invention.
The recording head further includes the return pole 84, coils 42,
and main pole 83 which form a magnetic circuit. In FIG. 17, the
return pole 84 consists of the soft magnetic multilayer 10 in which
ferromagnetic films are antiparallel coupled. Sets of the
ferromagnetic film 15 and antiparallel coupling film 153 are
layered in order. It is preferable to stack 2-12 layers of
ferromagnetic films 15 in the return pole. It is desirable to stack
an even number of ferromagnetic film layers so that magnetization
and reverse magnetization will cancel each other between adjacent
two among the ferromagnetic films disposed to be magnetized in
antiparallel directions. On the magnetic head, the air-bearing
surface 63 is formed which approaches a magnetic recording medium
and performs magnetic recording and readback.
FIG. 18 shows an example of structure of a perpendicular magnetic
recording head in which the soft magnetic multilayer in which
ferromagnetic films are antiferromagnetically coupled in accordance
with the present invention is employed to constitute the magnetic
shields. On the substrate 50 which is integrated with the slider,
the lower magnetic shield 35, one electrode 40, and the
magnetoresistive multilayer 101 are formed and, moreover, another
electrode 40 and the upper magnetic shield 36 are formed, and the
read gap 43 which senses a readback signal is formed.
While the TMR or CPP-GMR type readback sensor which causes current
to flow in the layer thickness direction is shown here as the
readback unit, it is possible to use another type of readback
sensor such as GMR readback sensors which cause current to flow in
the in-plane direction as the readback unit without altering the
essential characteristics of the present invention. The recording
head further includes the return pole 84, coils 42, and main pole
83 which form a magnetic circuit.
In FIG. 18, the lower magnetic shield 35 and upper magnetic shield
36 each consist of the soft magnetic multilayer 10 in which
ferromagnetic films are antiparallel coupled. Sets of the
ferromagnetic film 15 and antiparallel coupling film 153 are
layered in order. It is preferable to stack 2-12 layers of
ferromagnetic films 15 in the upper or lower magnetic shield. It
may be possible to constitute either the upper or lower shield or a
part thereof by the above soft magnetic multilayer without
contravening the essential characteristics of the present
invention.
It is desirable to stack an even number of ferromagnetic film
layers so that magnetization and reverse magnetization will cancel
each other between adjacent two among the ferromagnetic films
disposed to be magnetized in antiparallel directions. On the
magnetic head, the air-bearing surface 63 is formed which
approaches a magnetic recording medium and performs magnetic
recording and readback. Through constituting the magnetic shields
by the soft magnetic multilayer in which ferromagnetic films are
antiparallel coupled, variation in the read head output, induced by
the magnetic shields, can be reduced.
FIG. 19 shows an example of structure of a longitudinal magnetic
recording head in which the soft magnetic multilayer in which
ferromagnetic films are antiferromagnetically coupled in accordance
with the present invention is employed to constitute the tip of an
upper magnetic core. On the substrate 50 which is integrated with
the slider, the lower magnetic shield 35, one electrode 40, and the
magnetoresistive multilayer 101 are formed and, moreover, another
electrode 40 and the upper magnetic shield 36 are formed, and the
read gap 43 which senses a readback signal is formed.
While the TMR or CPP-GMR type readback sensor which causes current
to flow in the layer thickness direction is shown here as the
readback unit, it is possible to use another type of readback
sensor such as GMR readback sensors which cause current to flow in
the in-plane direction as the readback unit without altering the
essential characteristics of the present invention. The recording
head further includes a lower magnetic core 85, coils 42, a first
upper magnetic core 833, and a second upper magnetic core 834 which
form a magnetic circuit.
While, the upper magnetic core consists of the first and second
upper magnetic cores as shown here, the upper magnetic core may
consist of a single unit or three or more units without going
against the essential characteristics of the present invention.
Through constituting the magnetic core by the soft magnetic
multilayer in which ferromagnetic films are antiparallel coupled,
the following advantageous effects are obtained: stabilizing the
magnetic domain states in the ends, reducing post-recording noise,
and improving the shapes of the ends of recording magnetic
fields.
In FIG. 19, the first upper magnetic core 833 consists of the soft
magnetic multilayer 10 in which ferromagnetic films are
antiparallel coupled. Sets of the ferromagnetic film 15 and
antiparallel coupling film 153 are layered in order. It is
preferable to stack 2-12 layers of ferromagnetic films 15 in the
upper or lower magnetic core. It may be possible to constitute
either the upper magnetic core or lower magnetic core or a part
thereof by the above soft magnetic multilayer without contravening
the essential characteristics of the present invention, but it is
desirable to constitute the tip of the upper magnetic core by the
above soft magnetic multilayer. It is desirable to stack an even
number of ferromagnetic film layers so that magnetization and
reverse magnetization will cancel each other between adjacent two
among the ferromagnetic films disposed to be magnetized in
antiparallel directions. On the magnetic head, the air-bearing
surface 63 is formed which approaches a magnetic recording medium
and performs magnetic recording and readback.
FIG. 20 shows another example of structure of the soft magnetic
multilayer employed in the magnetic head of the present invention.
The soft magnetic multilayer 10 in which ferromagnetic films are
antiferromagnetically coupled is formed such that the underlayer 14
is formed on the substrate 50 and sets of the ferromagnetic film
15, the antiparallel coupling film 153, the ferromagnetic film 15,
and a decoupling film 154 are layered in order repeatedly. The
material, thickness, and deposition of the antiparallel coupling
film are adjusted so that antiferromagnetic coupling energy is
exerted to make adjacent ferromagnetic films 15 magnetized in
directions antiparallel with each other across the antiparallel
coupling film 153.
Meanwhile, the decoupling film 154 acts to separate adjacent
ferromagnetic films 15 and restrain these ferromagnetic films from
being magnetized in antiparallel with each other and coupling and
made of a different material from the antiparallel coupling film
153 or the same material as the antiparallel coupling film 153 but
being thick enough not to cause antiferromagnetic coupling. For
example, possible design is to interleave the ferromagnetic films
with 1 nm thick Cr antiparallel coupling films 153 and 1 nm thick
NiCr decoupling films 154 or 1 nm thick Cr antiparallel coupling
films 153 and 3 nm thick Cr decoupling films 154.
As illustrated by the structure example shown in FIG. 20, by
forming the soft magnetic multilayer such that each ferromagnetic
film 15 is antiferromagnetically coupled with one adjacent
ferromagnetic film 15 across an antiparallel coupling film 153 on
one interface and is not antiferromagnetically coupled with the
other adjacent ferromagnetic film 15 across a decoupling film 154
on the other interface, the soft magnetic multilayer with a high
permeability and moderated saturation magnetic field energy can be
obtained.
In the case of the soft magnetic multilayer structure shown in FIG.
1, each ferromagnetic film 15 is antiferromagnetically coupled with
two adjacent ferromagnetic films on either sides across
antiparallel coupling films 153 on both interfaces except the top
and bottom end ones and there are many interfaces contributing to
antiferromagnetic coupling, and, consequently, great saturation
magnetic field energy is generated. By contrast, in the
corresponding structure shown in FIG. 20, the number of the
interfaces for antiferromagnetic coupling can be reduced roughly by
half and the interfaces are arranged in kind of alternation, and,
therefore, saturation magnetic field energy can be moderated. The
soft magnetic multilayer illustrated in FIG. 20 can be applied to
different components of the magnetic head in the same manner as
described hereinbefore.
As other embodiments of the present invention, the following
magnetic heads were fabricated:
A magnetic head as a thin-film magnetic head for perpendicular
magnetic recording including a main pole with its tip facing a
magnetic recording medium, a return pole which forms a magnetic
circuit in conjunction with the main pole, and coils for exciting
the main pole, wherein at least a part of the return pole consists
of a soft magnetic multilayer containing laminations, each of which
comprises a first ferromagnetic film, a second ferromagnetic film,
and an antiparallel coupling layer formed between the first
ferromagnetic film and the second ferromagnetic film, wherein the
antiparallel coupling layer causes antiferromagnetic interlayer
coupling of the first ferromagnetic film and the second
ferromagnetic film.
A magnetic head which faces, in close proximity to, a magnetic
recording medium on which information has been recorded
magnetically, senses magnetic fields leaking from the recording
medium, and magnetically records information on the recording
medium, the magnetic head including a substrate, a lower magnetic
shield, a lower gap, a read element, an upper gap, and an upper
magnetic shield which are formed on the substrate, wherein the
lower magnetic shield and the upper magnetic shield form a magnetic
read gap of a predetermined clearance, wherein at least a part of
the lower magnetic shield and the upper magnetic shield consists of
a soft magnetic multilayer containing laminations, each of which
comprises a first ferromagnetic film, a second ferromagnetic film,
and an antiparallel coupling layer formed between the first
ferromagnetic film and the second ferromagnetic film, wherein the
antiparallel coupling layer causes antiferromagnetic interlayer
coupling of the first ferromagnetic film and the second
ferromagnetic film.
A magnetic head which faces, in close proximity to, a magnetic
recording medium on which information has been recorded
magnetically, senses magnetic fields leaking from the recording
medium, and magnetically records information on the recording
medium, the magnetic head including a substrate, a magnetic yoke,
and a read element which are formed on the substrate and a magnetic
circuit through which the magnetic yoke passes magnetic fields from
the recording medium surface on which the magnetic head faces on to
the read element is formed, wherein at least a part of the magnetic
yoke consists of a soft magnetic multilayer containing laminations,
each of which comprises a first ferromagnetic film, a second
ferromagnetic film, and an antiparallel coupling layer formed
between the first ferromagnetic film and the second ferromagnetic
film, wherein the antiparallel coupling layer causes
antiferromagnetic interlayer coupling of the first ferromagnetic
film and the second ferromagnetic film.
A magnetic head which faces, in close proximity to, a magnetic
recording medium on which information has been recorded
magnetically, senses magnetic fields leaking from the recording
medium, and magnetically records information on the recording
medium, wherein at least a part of magnetic cores or magnetic
shields of the magnetic head consists of a soft magnetic multilayer
containing laminations, each of which comprises a first
ferromagnetic film, a second ferromagnetic film, and an
antiparallel coupling layer formed between the first ferromagnetic
film and the second ferromagnetic film, wherein the first
ferromagnetic film and the second ferromagnetic film are made of
FeCo or FeCoNi alloy having a body centered cubic structure, the
antiparallel coupling layer causes antiferromagnetic interlayer
coupling of the first ferromagnetic film and the second
ferromagnetic film, the antiparallel coupling layer is made of Ru
or Ru alloy, and the thickness of the antiparallel coupling layer
falls within a range from 1.8 nm to 3 nm.
A magnetic head which faces, in close proximity to, a magnetic
recording medium on which information has been recorded
magnetically, senses magnetic fields leaking from the recording
medium, and magnetically records information on the recording
medium, wherein at least a part of magnetic cores or magnetic
shields of the magnetic head consists of a soft magnetic multilayer
containing laminations, each of which comprises a first
ferromagnetic film, a second ferromagnetic film, and an
antiparallel coupling layer formed between the first ferromagnetic
film and the second ferromagnetic film, wherein the first
ferromagnetic film and the second ferromagnetic film are made of
NiFe, CoFe or CoNiFe alloy having a face centered cubic structure,
the antiparallel coupling layer causes antiferromagnetic interlayer
coupling of the first ferromagnetic film and the second
ferromagnetic film, the antiparallel coupling layer is made of Ru
or Ru alloy, and the thickness of the antiparallel coupling layer
falls within a range from 0.5 nm to 1.2 nm.
Tests were made on the magnetic heads of the present invention
fabricated as described above and the magnetic recording and
readback devices on which these magnetic heads are mounted and the
test results indicated sufficient outputs, good recording/readback
performances, and quite reliable operation.
As detailed hereinbefore, magnetic heads featuring stable
magnetization can be obtained in accordance with the present
invention. Especially, perpendicular magnetic recording heads in
which "erase after write" faults are restrained can be
obtained.
* * * * *